1. Field of the Invention
This invention relates to a muffler holding member retaining a muffler to an automotive body and absorbing the vibrations caused by the operation of the internal combustion engine of an automobile and transmitted from the muffler or automotive body.
2. Description of the Prior Art
FIG. 5 illustrates an well-known conventional type muffler holding member. This conventional type muffler holding member is a elliptical-shaped, plate type member and made of an elastic material. The conventional type muffler holding member in FIG. 5 has a structure comprising: a first holding part 1a having a first through hole 10a into which a supporting member of an automotive body side is to be inserted, a second holding part 2a formed with a space between said first holding part 1a and having a second through hole 20a into which a supporting member of a muffler side is to be inserted, and a pair of side parts 3a connecting the first holding part 1a and the second holding part 2a at the both sides thereof.
In FIG. 6, another conventional type muffler holding member is illustrated. This type of the muffler holding member is disclosed in the Japanese Unexamined Utility Model Publication (KOKAI) No. 59-186574. In this prior art arrangement, a metal rod is provided as a mass member 4b which is connected to the each side part 3b at the central portion thereof. Accordingly, the mass member 4b resonates with the elastic material composing the muffler holding member. In effect, the vibration transmissibility is gradually absorbed to a zero level. In accordance with this type of the conventional muffler holding member, the vibration transmissibility in the major-axial direction can be lowered. (Hereinafter, the major-axial direction shall mean the direction connecting the first through hole 10a and the second through hole 20a, and the minor-axial direction shall mean the direction connecting the both side parts 3a).
According to the muffler holding member of the conventional type shown in FIG. 5, vibrations caused by the operation of the internal combustion engine and transmitted from the muffler or from the automotive body can be absorbed by the elastic material composing the muffler holding member. However, when tensile/compression stresses are working in the muffler holding member in the major-axial direction, the tensile/compression stresses are applied to the pair of side parts 3a and a part of the tensile/compression stresses is applied as bending stress to the side part 3a. Consequently, a phenomenon of surging occurs by which the pair of side parts 3a vibrates in the minor-axial direction. And if each side part 3a vibrates oppositely in direction by another type of the surging, vibration transmissibility of the muffler holding member in the major-axial direction is increased. As a result of the phenomenon, vibrations at a part apt to be transmitted to other part as well and thereby, the vibration absorbing effect of the muffler holding member is greatly reduced. Generally, vibration transmissibility (absolute spring constant) of the conventional type muffler holding member shown in FIG. 5 is increased at a frequency level exceeding 500 Hz.
On the other hand, the other type of the conventional muffler holding member shown in FIG. 6 is usually effective in lowering the vibration transmissibility at a high frequency level, namely, the frequency exceeding 500 Hz, by the effect of the resonance of the mass member 4b. However, in this type, vibration transmissibility is greatly increased at the frequency level (usually about 200 Hz) corresponds to the intrinsic vibration frequency of the mass member 4b.
In addition, since the mass member 4b vibrates in the minor-axial direction, the vibrations are transmitted to the major-axial direction of the muffler holding member through the side parts 3b forming the muffler holding member. As a result of this effect, rigidity of the muffler holding member in the major-axial direction is decreased.
Further, owing to the presence of the mass member 4b, the vibration transmissibility of the muffler holding member in the major-axial direction tends to increase.
Still further, the frequency of the resonance is changed as the temperature changes, so that the adjustment of tunning is difficult.
Still further, if the mass member 4b is disposed at a slant to the muffler holding member, the resonance direction is changed. Accordingly, the mounting of the mass member 4b to the muffler holding member requires careful manner.